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Rakesh Kumar Jha,Kanghae Kim,Mansik Jeon,JeeHyun Kim,Min Young Kang,Insook Han,Moonkyu Kim 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.5
Swept-source optical coherence tomography (SS-OCT), a bio-photonic imaging modality, was used to demonstrate an initial feasibility experiment for detecting morphological variations of invivo mouse hair follicles for the anagen and the telogen growth stages. Two C57BL/6 adult male mice, one undergoing the anagen stage and the other undergoing the telogen stage of the hair follicle growth cycle, were selected for the experiment. The OCT cross-sectional images of mice skin were acquired in-vivo within an interval of 15 days, and the observed morphological changes were analyzed. The micro-structural features of mice skin on the 15th experimental day were further compared with corresponding histological observations. The preliminary result of this study provides clear insights into the structural details of mouse skin, confirming the resemblance of the OCT images with the corresponding histological measurements, and ensures the suitability of SSOCT for non-invasive analysis of hair follicle conditions.
Kim, Whi Dong,Baum, Fá,bio,Kim, Dahin,Lee, Kangha,Moon, Jun Hyuk,Lee, Doh C. The American Chemical Society 2014 CRYSTAL GROWTH AND DESIGN Vol.14 No.3
<P>We report the transformation of several metal selenide nanocrystals (NCs), including PbSe, CdSe, ZnSe, and PbSe/CdSe core/shell NCs, in dimethyl sulfoxide (DMSO) in acidic solutions at room temperature. In this study, the DMSO solution of metal selenide NCs was mixed with nitric acid, which was used to adjust the pH of the solution. Upon mixing, the metal selenide NCs readily transformed into crystalline selenium (trigonal structure) nano- or microwires under ambient light, whereas little or no transformation occurred in the dark. Photocorrosion, where the photogenerated carriers within the NCs participate in the cleavage of the metal and selenium atoms, turns out to be responsible for the transformation. DMSO removes organic ligands on the NC surface and creates surface trap sites for photoinduced charge carriers. Then, nitric acid helps shift the reduction potentials, thereby promoting a “cathodic reduction”. In this sense, the photocorrosion rate can be controlled by several parameters, such as the absorption cross section of the selenide NCs and the pH. The diameter and shape of the resulting selenium wires help gauge the transformation rate and thus unveil the transformation mechanism.</P><P>Semiconductor selenide nanocrystals transform into crystalline selenium nanowires after mixing with dimethyl sulfoxide in acidic solution. The transformation appears to occur via photocorrosion, whose kinetics depends upon the energy gap of the original selenide nanocrystals.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cgdefu/2014/cgdefu.2014.14.issue-3/cg4017849/production/images/medium/cg-2013-017849_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cg4017849'>ACS Electronic Supporting Info</A></P>
Kim, Whi Dong,Lee, Sooho,Pak, Chaewon,Woo, Ju Young,Lee, Kangha,Baum, Fá,bio,Won, Jonghan,Lee, Doh C. The Royal Society of Chemistry 2014 Chemical communications Vol.50 No.14
<P>We report ripening of metal particles anchored on pyramid-shaped heterostructure nanocrystals. The ‘intra-particle’ ripening results in a large metal tip at one corner with the other three tips vanishing. Investigation reveals that the ripening and core/shell formation affects photocatalytic activities <I>via</I> the Fermi level change.</P> <P>Graphic Abstract</P><P>The Ostwald ripening of metal nanoparticles on pyramid-shaped nanocrystals is elucidated. The controlled overgrowth of the metal shell on existing metal cocatalysts enables the study of the effects of the Fermi level upon photocatalysis using heterostructure nanocrystals. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cc48919a'> </P>
Lee, Kangha,Lee, Cheol-Ho,Cheong, Jun Young,Lee, Seokwon,Kim, Il-Doo,Joh, Han-Ik,Lee, Doh Chang Springer-Verlag 2017 Korean Journal of Chemical Engineering Vol.34 No.12
<P>We report photoelectrochemical hydrogen evolution reaction using a Cu2O-based photocathode with a layer doped with Zn ions. The doping results in the shift of the onset flat-band potential of the photocathode, likely a consequence of maximized band-bending in the Cu2O/Zn : Cu2O heterojunction. Systematic electrochemical analysis reveals that expansion of depletion region is responsible for the enhanced photoelectrochemical performance, e.g., the increase of photocurrent and reduced internal resistance.</P>
Cho, Hyunjin,Kim, Whi Dong,Lee, Kangha,Lee, Seokwon,Kang, Gil-Seong,Joh, Han-Ik,Lee, Doh C. Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.429 No.-
<P><B>Abstract</B></P> <P>We investigate the product selectivity of CO<SUB>2</SUB> reduction using NiO photocathodes decorated with CdSe quantum dots (QDs) of varying size in a photoelectrochemical (PEC) cell. Size-tunable and quantized energy states of conduction band in CdSe QDs enable systematic control of electron transfer kinetics from CdSe QDs to NiO. It turns out that different size of CdSe QDs results in variation in product selectivity for CO<SUB>2</SUB> reduction. The energy gap between conduction band edge and redox potential of each reduction product (<I>e.g.</I>, CO and CH<SUB>4</SUB>) correlates with their production rate. The size dependence of the electron transfer rate estimated from the energy gap is in agreement with the selectivity of CO<SUB>2</SUB> reduction products for all reduction products but CO. The deviation in the case of CO is attributed to sequential conversion of CO into CH<SUB>4</SUB> with CO adsorbed on electrode surface. Based on a premise that the CdSe QDs would exhibit similar surface configuration regardless of QD size, it is concluded that the electron transfer kinetics proves to alter the selectivity of CO<SUB>2</SUB> reduction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Size-tunable energy states of conduction band in CdSe quantum dots enable systematic control of product selectivity for CO<SUB>2</SUB> reduction. </LI> <LI> The energy gap between conduction band edge and redox potential of each reduction product correlates with their production rate. </LI> <LI> The electron transfer kinetics proves to alter the selectivity of CO<SUB>2</SUB> reduction. </LI> </UL> </P>
Koh, Sungjun,Eom, Taedaehyeong,Kim, Whi Dong,Lee, Kangha,Lee, Dongkyu,Lee, Young Kuk,Kim, Hyungjun,Bae, Wan Ki,Lee, Doh C. American Chemical Society 2017 Chemistry of materials Vol.29 No.15
<P>Growth of monodisperse indium phosphide (InP) quantum dots (QDs) represents a pressing demand in display applications, as size uniformity is related to color purity in display products. Here, we report the colloidal synthesis of InP QDs in the presence of Zn precursors in which size uniformity is markedly enhanced as compared to the case of InP QDs synthesized without Zn precursors. Nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and mass spectrometry analyses on aliquots taken during the synthesis allow us to monitor the appearance of metal phosphorus complex intermediates in the growth of InP QDs. In the presence of zinc carboxylate, intermediate species containing Zn-P bonding appears. The Zn-P intermediate complex with P(SiMe3)(3) exhibits lower reactivity than that of the In P complex, which is corroborated by our prediction based on density functional theory and electrostatic potential charge analysis. The formation of a stable Zn P intermediate complex results in lower reactivity, which enables slow growth of QDs and lowers the extreme reactivity of P(SiMe3)(3), hence monodisperse QDs. Insights from experimental and theoretical studies advance mechanistic understanding and control of nucleation and growth of InP QDs, which are key to the preparation of monodisperse InP-based QDs in meeting the demand of the display market.</P>
Lee, Sooho,Lee, Kangha,Kim, Whi Dong,Lee, Seokwon,Shin, Do Joong,Lee, Doh C. American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.41
<P>In this study, we designed and synthesized photocatalysts for hydrogen evolution from water by coating a thin layer of amorphous TiO<SUB>2</SUB> (<I>a</I>-TiO<SUB>2</SUB>) on CdSe nanocrystals (NCs). The thin shell of <I>a</I>-TiO<SUB>2</SUB> serves as a channel for charge carriers otherwise unutilized. Albeit a previous notion that <I>a</I>-TiO<SUB>2</SUB> is a poor photocatalyst, the enhanced photocatalytic activity in the presence of <I>a</I>-TiO<SUB>2</SUB> suggests that the material helps utilize the photogenerated charge carriers when it is in a form of thin shell on CdSe NCs. Type II band offset in CdSe/<I>a</I>-TiO<SUB>2</SUB> appears to allow the electron in the conduction band of CdSe NCs to migrate over to that of <I>a</I>-TiO<SUB>2</SUB>, and the electron participates in the hydrogen production from water. Size of CdSe NCs influences the photocatalytic hydrogen evolution rate as the energy difference between the conduction bands of semiconductors becomes larger. Electron transfer from CdSe NCs to <I>a</I>-TiO<SUB>2</SUB> layer is influenced by the level of the conduction-band edge of CdSe NCs: the size dependence indicates that electron injection to TiO<SUB>2</SUB> is facilitated with energy level offset between CdSe and TiO<SUB>2</SUB>, while smaller NCs have larger band gap and thus narrower spectral range of absorption. The interplay between charge-transfer rate and absorption cross-section should be considered in designing heterostructure NC-based photocatalysts for water splitting.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-41/jp508315m/production/images/medium/jp-2014-08315m_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp508315m'>ACS Electronic Supporting Info</A></P>